Mineral Formation

• Minerals form through various processes in nature.
  • They can form from
    1. magma,
    2. fluids,
    3. metamorphism,
    4. precipitation,
    5. weathering,
    6. and organic processes.

1. Minerals Formation from Magma

Mechanism:
- Crystallization occurs as magma cools.
- As temperature decreases, minerals crystallize in a specific order based on their melting points (Bowen’s Reaction Series).

Examples:
- Olivine (high-temperature crystallization)
- Quartz (low-temperature crystallization)

2. Minerals Formation from Fluids

Mechanism:
- Minerals precipitate from hydrothermal fluids or gases that escape from cooling magma.
- The fluids interact with rocks and cool, allowing mineral crystals to form.

Examples:
- Gold and sulfide minerals (from hydrothermal fluids)
- Chalcedony (from silica-rich fluids)

3. Minerals Formation by Metamorphism

Mechanism:
- Heat and pressure during metamorphism cause minerals in existing rocks to recrystallize or form new minerals.

Examples:
- Garnet (high pressure and temperature)
- Kyanite (forms during regional metamorphism)

4. Precipitation from Aqueous Solution

Mechanism:
- As water evaporates, minerals dissolved in the solution crystallize.

Examples:
- Halite (from evaporating saltwater)
- Gypsum (from evaporating water)

5. Precipitation from Gaseous Emanations

Mechanism:
- Hot gases escaping from volcanic vents deposit minerals directly onto the Earth’s surface.

Examples:
- Sulfur (around volcanic fumaroles)
- Sal ammoniac (rare, forms from volcanic gases)

6. Weathering: Alteration of Minerals

Mechanism:
- Weathering processes break down minerals, and some may alter to more stable forms at Earth’s surface.

Examples:
- Feldspar weathering to kaolinite (a clay mineral)
- Biotite weathering to chlorite

7. Organic Formation of Minerals

Mechanism:
- Organisms form minerals within their shells, bones, or teeth. These minerals, though organic, are still classified as minerals because they can form inorganically as well.

Examples:
- Calcite (in shells of marine organisms)
- Apatite (in bones and teeth)

Isomorphism, Polymorphism, and Pseudomorphism

Isomorphism

Definition:
- Occurs when minerals have the same crystal structure but different chemical compositions.

Example:
- Olivine group (Fe and Mg can substitute in the crystal lattice)

Polymorphism

Definition:
- Minerals with the same chemical composition but different crystal structures.

Examples:
- Diamond and Graphite (both made of carbon, but different structures)
- Calcite and Aragonite (both made of calcium carbonate)

Pseudomorphism

Definition:
- One mineral replaces another while retaining the external form of the original mineral.

Example:
- Limonite replacing pyrite (retains pyrite’s cubic shape)